This invention relates generally to golf balls, and more specifically, to a golf ball having a hoop-stress layer within a layered rubber construction. In particular, it is directed to a golf ball having multiple layers including a center of at least one layer of a resilient elastomeric material, a hoop-stress layer including at least one material with a tensile elastic modulus of at least about 10,000 kpsi, and an outermost layer of a thermosetting material. The golf balls of the present invention can provide decreased spin and improved resiliency for better distance, as well as maintaining the xe2x80x9csoftxe2x80x9d feel of a traditional wound ball.
Until recently, golf balls were typically divided into two general types or groups: 1) two piece balls and 2) wound balls (also known as three piece balls). The difference in play characteristics resulting from these different types of constructions can be quite significant.
Balls having a two piece construction are generally most popular with the recreational golfer because they provide a very durable ball while also providing maximum distance. Two piece balls are made with a single solid core, usually formed of a crosslinked rubber, which is encased by a cover material. Typically the solid core is made of polybutadiene which is chemically crosslinked with zinc diacrylate and/or similar crosslinking agents. The cover comprises tough, cut-proof blends of one or more materials known as ionomers such as SURLYN(copyright), which are resins sold commercially by DuPont or IOTEK(copyright) which is sold commercially by Exxon.
The combination of the above-described core and cover materials provides a xe2x80x9chardxe2x80x9d covered ball that is resistant to cutting and other damage caused by striking the ball with a golf club. Further, such a combination imparts a high initial velocity to the ball which results in increased distance. Due to their hardness however, these balls have a relatively low spin rate which makes them difficult to control, particularly on shorter approach shots. As such, these types of balls are generally considered to be xe2x80x9cdistancexe2x80x9d balls. Because these materials are very rigid, many two piece balls have a hard xe2x80x9cfeelxe2x80x9d when struck with a club. Softer cover materials such as balata and softer ionomers in some instances, have been employed in two piece construction balls in order to provide improved xe2x80x9cfeelxe2x80x9d and increased spin rates.
Wound balls typically have either a solid rubber or fluid center around which many yards of a tensioned elastic thread, typically polyisoprene, are wrapped to form a wound core. The wound core is then covered with a durable cover material such as a SURLYN(copyright), or similar material, or a softer cover such as balata. A wound material layer differs from a solid layer in that the wound layer is often able to more readily elongate and compress in a direction lateral to the impacting force. For this reason, wound golf balls have a tendency to more easily compress at impact and have more spin, as compared to a solid golf ball (Dalton, Golf and Science III, 1999), which enables a skilled golfer to have more control over the ball""s flight. In particular, it is desirable that a golfer be able to impart back spin to a golf ball for purposes of controlling its flight and controlling the action of the ball upon landing on the ground. For example, substantial back spin will make the ball stop once it strikes the landing surface instead of bounding forward. The ability to impart back spin onto a golf ball is related to the extent to which the golf ball cover deforms when it is struck with a golf club. Because wound balls are traditionally more deformable than conventional two piece balls, it is easier to impart spin to wound balls. However, wound higher spinning balls typically travel a shorter distance when struck as compared to a two piece ball. Moreover, as a result of their more complex structure, wound balls generally require a longer time to manufacture and are more expensive to produce than a two piece ball.
Therefore, golf ball manufacturers are continually searching for new ways in which to provide golf balls that deliver the maximum performance in terms of both distance and spin rate for golfers of all skill levels.
Golf ball designs have been introduced which use multilayer non-wound constructions in an effort to overcome some of the undesirable aspects of conventional two piece balls and wound balls, while maintaining the positive attributes of these golf balls (including their increased initial velocity and distance). These include double cover designs with solid, single member cores; dual core designs with two core members and a single cover layer; and balls with multiple core and/or multiple cover layers.
A number of patents have been issued directed towards modifying the properties of a conventional two piece ball by altering the typical single layer core and/or single cover layer construction to provide a multilayer core and/or cover. The inventions disclosed in these patents are directed towards improving a variety of golf ball characteristics.
One technique suggested in the prior art to avoid the problem of an overly hard stiff cover was disclosed in U.S. Pat. No. 4,431,193 issued to Nesbitt. Rather than have a single layer cover over the core, the cover would be molded in two layers: a hard stiff inner layer of a high flexural modulus material that provides significant hoop stress, surrounded by a soft, flexible outer cover of a lower flexural modulus material of approximately 14 kpsi. Balls of this design have been sold bearing the Strata name for some time, however, because of the inner layer thickness of about 0.045 inches to 0.050 inches and the high flexural modulus of greater than 50,000 psi, the golf balls have a hard feel to which many golfers object.
U.S. Pat. No. 5,072,944 discloses a three-piece solid golf ball having a center and outer layer which are prepared from a rubber composition, preferably having a base rubber of polybutadiene. This patent teaches that it is desirable that the center core is softer than the outer layer, wherein the layers have a hardness (Shore C) of 25-50 and 70-90 respectively.
U.S. Pat. No. 5,002,281 is directed towards a three-piece solid golf ball which has an inner core having a hardness of 25-70 (Shore C) and an outer shell having a hardness of 80-95 (Shore C), wherein the specific gravity of the inner core must be greater than 1.0, but less than or equal to that of the outer shell, which must be less than 1.3.
Additionally, several patents have been issued which employ a wound layer of high tensile elastic modulus material, thus replacing the need for a cover providing the necessary hoop-stress in a golf ball.
U.S. Pat. No. 5,713,801 issued to Aoyama teaches a method for making a golf ball providing a core of solid resilient material, winding a high elastic modulus fiber on the core to create a first wound layer to form a xe2x80x9choop-stress layer,xe2x80x9d and molding an outer layer of resilient material about the first wound layer. The core in the above method and apparatus may also be made of a center wound with a low modulus fiber and provided with an initial tension. The preferred cover materials are ionomer and balata.
U.S. Pat. No. 5,913,736 issued to Maehara et al. builds upon Aoyama to describe a hoop-stress layer made of a shape memory alloy (Tixe2x80x94Ni) wound around a core so as to provide a shaped memory alloy layer.
The golf ball of the present invention has three or more concentrically disposed layers, including: a core, preferably polybutadiene, of at least one layer formed of at least one resilient elastomeric material; a hoop-stress layer including at least one material, preferably wire, thread, or filament, under a tensile elastic modulus of at least about 10,000 kpsi, preferably at least about 20,000 kpsi, wound or wrapped about the core; and an outermost thermoset material of at least one layer disposed about the hoop-stress layer and having a thickness of greater than about 0.065 inches.
The material forming the hoop-stress layer is preferably a continuous strand of diameter ranging from about 0.004 to 0.04 inches. The material can be glass, aromatic polyamids, carbon, metals, shape memory alloys, natural fibers, or a combination thereof and can be wound or wrapped in a criss-cross, basket weave, or open pattern about the core. When wound or wrapped, the material can include a plurality of braided elements.
The outermost thermoset material includes at least one of polybutadiene, natural rubber, styrene butadiene rubber, isoprene, or mixtures thereof and a hardness from about 10 to 90 Shore D. In one embodiment, the outermost thermoset material includes polybutadiene. The outermost layer can have a thickness of 0.065 inches, preferably 0.08 inches, and most preferably 0.1 inches. The outermost layer can include an abrasion resistant material.
In one embodiment, the golf ball further includes a second resilient elastomeric material of at least one layer disposed between the hoop-stress layer and the outermost thermoset material.
The first resilient elastomeric material and the outermost thermoset material can each comprise polybutadiene. In one embodiment, the polybutadiene used in the first resilient elastomeric material and the outermost thermoset material is the same. Another embodiment of the invention is a golf ball having four or more concentrically disposed layers, including: a core of at least one layer formed from a resilient elastomeric material; an outermost thermoset material of at least one layer, having a thickness greater than about 0.065 inches, preferably greater than about 0.08 inches, disposed about the second resilient elastomeric material of at least one layer; and hoop-stress layer formed from at least one wound material with a tensile elastic modulus of at least about 10,000 kpsi, preferably at least about 20,000 kpsi, disposed between the core and the outermost thermoset material, wherein the at least one material forming the hoop-stress layer has a first cross-sectional area and is coated with a binding material layer to create a second cross-sectional area greater than the first.
In this aspect of the invention, the material forming the hoop-stress layer can be a continuous strand of diameter ranging from about 0.004 to about 0.04 inches.
The binding material can include at least one of thermoplastic polyvinyl butyral, thermoplastic epoxy, thermoplastic polyester phenolic, thermoplastic polyamide, thermosetting adhesive epoxy, thermoplastic polyamide-imide, or combinations thereof. The second cross-sectional area is preferably at least about 5 percent larger than the first cross-sectional area.
The outermost thermoset material includes at least one of polybutadiene, natural rubber, and styrene butadiene rubber, isoprene, or mixtures thereof.